Explain why?
(i) The blood pressure in humans is greater at the feet than the brain.
(ii) Atmospheric pressure at a height of about 6 km decreases to nearly half its value at the sea level though the height of the atmosphere is more than 100 km.
(iii) Hydrostatic pressure is a scalar quantity even though pressure is force divided by area.
(i) The pressure of liquid column is given by p = hpg, where h is depth, p is density and g is acceleration due to gravity.
Therefore, pressure of liquid column increases with depth. The height of blood column in human body is more at feet than at the brain. Therefore, the blood pressure in humans is greater at the feet than the brain.
(ii) The density of air is maximum near the surface of the earth and decreases rapidly with height. At a height of 6 km, the density of air decreases to nearly half of its value at the sea level. Beyond 6 km height, the density of air decreases very slowly with height. Hence, the atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the sea level.
(iii) When force is applied on a liquid, the pressure is transmitted equally in all directions inside the liquid. Therefore, hydrostatic pressure has no fixed direction and hence, it is a scalar quantity.